U.S. patent application number 14/404093 was filed with the patent office on 2015-06-18 for multilayer aluminium brazing sheet for fluxfree brazing in controlled atmosphere.
This patent application is currently assigned to Granges Sweden AB. The applicant listed for this patent is Granges Sweden AB. Invention is credited to David Abrahamsson, Linda Ahl, Richard Westergard.
Application Number | 20150165564 14/404093 |
Document ID | / |
Family ID | 48700674 |
Filed Date | 2015-06-18 |
United States Patent
Application |
20150165564 |
Kind Code |
A1 |
Ahl; Linda ; et al. |
June 18, 2015 |
MULTILAYER ALUMINIUM BRAZING SHEET FOR FLUXFREE BRAZING IN
CONTROLLED ATMOSPHERE
Abstract
An aluminium brazing sheet comprising an aluminium alloy core
material covered by an interlayer and an Al--Si braze alloy is
disclosed. The interlayer consists of an aluminium alloy comprising
.ltoreq.1.0% Si and 0.1-2.5% Mg. The Al--Si braze alloy comprises
5-14% Si and 0.01-1.0% Bi. The core material and the interlayer has
a higher melting temperature than the braze alloy.
Inventors: |
Ahl; Linda; (Svartinge,
SE) ; Westergard; Richard; (Finspang, SE) ;
Abrahamsson; David; (Finspang, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Granges Sweden AB |
Finspang |
|
SE |
|
|
Assignee: |
Granges Sweden AB
Finspang
SE
|
Family ID: |
48700674 |
Appl. No.: |
14/404093 |
Filed: |
May 28, 2013 |
PCT Filed: |
May 28, 2013 |
PCT NO: |
PCT/SE2013/050606 |
371 Date: |
November 26, 2014 |
Current U.S.
Class: |
428/654 ;
228/101 |
Current CPC
Class: |
C22C 21/02 20130101;
B23K 35/002 20130101; B23K 2103/10 20180801; B23K 1/012 20130101;
B23K 35/286 20130101; B23K 35/288 20130101; Y10T 428/12764
20150115; B32B 15/20 20130101; B32B 15/043 20130101; C22C 21/00
20130101; C22C 21/08 20130101; B32B 15/016 20130101; F28F 21/089
20130101; B32B 2250/03 20130101; B23K 35/0238 20130101; C22C 21/06
20130101; B23K 1/0012 20130101 |
International
Class: |
B23K 35/02 20060101
B23K035/02; B23K 35/00 20060101 B23K035/00; B23K 35/28 20060101
B23K035/28; B32B 15/20 20060101 B32B015/20; C22C 21/02 20060101
C22C021/02; C22C 21/08 20060101 C22C021/08; B32B 15/04 20060101
B32B015/04; B23K 1/00 20060101 B23K001/00; C22C 21/00 20060101
C22C021/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2012 |
SE |
1250566-5 |
Claims
1. An aluminium alloy brazing sheet for fluxfree brazing suitable
for brazing to other components, the aluminium alloy brazing sheet
comprising: an aluminium alloy core material covered by an
interlayer of an aluminium alloy comprising .ltoreq.1.0 wt-% Si and
0.1-2.5 wt-% Mg, the interlayer being covered by an Al--Si braze
alloy which comprises 5-14 wt-% Si, <0.02 wt-% Mg, 0.01-1.0 wt-%
Bi, .ltoreq.0.8 wt-% Fe, .ltoreq.6 wt-% Zn, .ltoreq.0.1 wt-% Sn,
.ltoreq.0.1 wt-% In, .ltoreq.0.3 wt-% Cu, .ltoreq.0.15 wt-% Mn,
.ltoreq.0.05 wt-% Sr, and unavoidable impurities each in amounts
less than 0.05 wt-% and a total impurity content of less than 0.2
wt-%, the balance consisting of aluminium, wherein said core
material and the interlayer have a higher melting temperature than
the braze alloy, and wherein the interlayer is sacrificial to the
core material.
2. An aluminium alloy brazing sheet according claim 1, where the
interlayer alloy contains: Mg 0.1-2.5 wt-%, Mn<2.0 wt-%,
Cu.ltoreq.1.2 wt-%, Fe.ltoreq.1.0 wt-%, Si.ltoreq.1.0 wt-%,
Ti.ltoreq.0.2 wt-%, Zn.ltoreq.6 wt-%, Sn.ltoreq.0.1 wt-%,
In.ltoreq.0.1 wt-%, and Zr, Cr, V and/or Sc.ltoreq.0.2 wt-% in
total, and unavoidable impurities each in amounts less than 0.05
wt-%, and a total impurity content of less than 0.2 wt-%, the
balance consisting of aluminium.
3. An aluminium alloy brazing sheet according to claim 1, where the
core material is a 3XXX alloy.
4. An aluminium alloy brazing sheet according to claim 1, where the
Al--Si braze alloy contains 0.05 to 0.5 wt-% Bi.
5. An aluminium alloy brazing sheet according to claim 1, where the
Al--Si braze alloy contains <0.01 wt-% Mg.
6. An aluminium alloy brazing sheet according to claim 1, where the
Al--Si braze alloy contains 7 to 13 wt-% Si.
7. An aluminium alloy brazing sheet according to claim 1, where the
melting point of the interlayer and that of the core is
>615.degree. C.
8. An aluminium alloy brazing sheet according to claim 1, where the
melting point of the braze alloy is 550-590.degree. C.
9. An aluminium alloy brazing sheet according to claim 1, where the
thickness of the interlayer to the thickness of the braze alloy
layer is 25-250%.
10. An aluminium alloy brazing sheet according to claim 1, where
the thickness of the interlayer is 5-200 .mu.m.
11. An aluminium alloy brazing sheet according to claim 1, where
the brazing sheet has a braze or a sacrificial clad layer on the
side of the core opposite the side comprising the interlayer and
the braze alloy.
12. An aluminium alloy brazing sheet according to claim 11, where
the sacrificial clad on the opposite side of the core is covered by
a sacrificial or braze layer.
13. A brazed product comprising an aluminium alloy brazing sheet
according to claim 1, wherein the interlayer is sacrificial to the
core.
14. Method of brazing a heat exchanger without using flux using the
aluminium alloy brazing sheet of claim 1 for the fins, tubes or
header plates.
15. Heat exchanger comprising an aluminium brazing sheet according
to claim 1.
16. Method for producing a heat exchanger, the method comprising
using an aluminium alloy brazing sheet according to claim 1.
17. An aluminium alloy brazing sheet according to claim 1, where
the core material is a 3XXX alloy containing: Mn<2.0 wt-%,
Cu.ltoreq.1.2 wt-%, Fe.ltoreq.1.0 wt-%, Si.ltoreq.1.0 wt-%,
Ti.ltoreq.0.2 wt-%, Mg.ltoreq.2.5 wt-%, Zr, Cr, V and/or
Sc.ltoreq.0.2 wt-% in total, and unavoidable impurities each in
amounts less than 0.05 wt-% and a total impurity content of less
than 0.2 wt-%, the balance consisting of aluminium.
18. An aluminium alloy brazing sheet according claim 17, where the
3XXX alloy contains 0.03-2.0 wt-% Mg.
19. An aluminium alloy brazing sheet according claim 2, where the
interlayer alloy contains 0.5-2.5 wt-% Mg.
20. An aluminium alloy brazing sheet according claim 3, where the
core material contains 0.03-2.0 wt-% Mg.
21. An aluminium alloy brazing sheet according claim 4, where the
Al--Si braze alloy contains 0.07 to 0.2 wt-% Bi.
22. An aluminium alloy brazing sheet according to claim 9, where
the thickness of the interlayer to the thickness of the braze alloy
layer is 50-150%.
Description
FIELD OF INVENTION
[0001] The present invention relates to a multilayer aluminium
brazing sheet comprising a core material covered with an
interlayer, and an outer covering braze layer. The invention also
relates to a heat exchanger comprising said improved multilayered
aluminium brazing sheet.
BACKGROUND
[0002] The present invention relates to sheet materials for joining
by means of brazing of aluminium materials in an inert or reducing
atmosphere, generally at atmospheric pressure, without the need to
apply a flux to break up, dissolve or dislodge the superficial
oxide layer.
[0003] A challenge today is to design and manufacture materials and
components for the heat exchanger industry at as low final cost and
with as high quality as possible. The most commonly used technology
in production of heat exchangers is brazing in a controlled
atmosphere normally consisting of nitrogen with as low amounts of
oxidising impurities (primarily oxygen gas and water vapour) as
possible. This process is known as controlled atmosphere brazing
("CAB") and involves the application of an Al--K--F based flux,
e.g. Nocolok flux, on the surfaces to be joined prior to brazing.
The flux breaks up, dislodges or dissolves the superficial oxide
layer of the filler metal to facilitate wetting between a molten
filler and the surfaces of individual heat exchanger components.
The flux also prevents or reduces formation of new oxides during
the joint formation. Post-brazed flux residues are, however, often
considered to be harmful for the heat exchanger as they may detach
from the brazed aluminium surfaces and clog internal channels,
thereby preventing an effective use of the heat exchanger.
Sometimes arguments are heard that the use of flux in some cases
promotes corrosion and erosion and lead to less effective units and
sometimes premature failure of the unit. There are also concerns
related to chemical reactions taking place between flux residue and
corrosion inhibitors used in the medium in e.g. the radiator
circuit that may cause damage to the system. Apart from the purely
function related drawbacks of flux usage, the impact of flux and
fluxing on e.g. the working environment, cost, investments in
brazing related hardware and it's maintenance, energy and the
natural environment is severe.
[0004] In addition to above mentioned limitations, the oxide
removal efficiency of a CAB flux is reduced by the use of Mg as an
alloying element in the material to be brazed. This is due to a
reaction between Mg and the flux forming compounds that have a very
high melting temperature and that prevent wetting, fillet formation
and joint growth. This incompatibility is troublesome as Mg is very
efficient when it comes to providing strength in aluminium
materials. Consequently, CAB has been constrained to non heat
treatable (NHT) alloys and alloys that contain a low amount of Mg.
It is well known that Mg starts to affect brazing outcome already
at trace levels and at levels of 0.2% the majority of CAB users
have large problems with joint formation. The problem can be
contained to some extent by increasing the additions of flux or by
the use of exclusive and costly Cs-containing flux grades. The
problem is, however, not solved but rather shifted towards
marginally higher Mg levels.
[0005] To be able to produce heat exchangers using CAB without the
application of flux, development of new material concepts and
designs is thus necessary to make braze joint formation
possible.
[0006] All temper and alloy designations hereafter used refer to
the Aluminium Association designation Standards and Data and the
Registration Records as published by the Aluminium Association in
2007. All percentages with respect to chemical content in an alloy
is henceforth understood to denote the weight percentage.
[0007] The patent EP1306207B1 describes an aluminium brazing alloy
suitable for brazing in an inert gas without the use of a flux.
This invention is based on a multi layered brazing sheet, where the
outer material is a thin covering layer covering an Al--Si based
alloy containing 0.1 to 0.5% Mg and 0.01 to 0.5% Bi, and a core
material. During the temperature ramp up stage of a braze cycle the
intermediate Al--Si layer will first start to melt and expand
volumetrically to break up the thin covering layer allowing molten
filler metal to seep through the cracks and on to the surface of
the brazing sheet.
[0008] In WO2008/155067A1 a method for brazing without flux is
disclosed. The invention is based on a multilayered aluminium sheet
comprising a thin covering layer, an Al--Si brazing material as
intermediate layer between the covering layer and the core. The
covering alloy and the core alloy have a solidus temperature higher
than the liquidus temperature of the brazing material. The Al--Si
brazing alloy contains 0.01-0.09% Mg and 0.01-0.5% Bi. The content
of Mg of the core is preferably <0.015%. In this document
fluxless brazing is made possible by keeping the total Mg content
of the brazing sheet less than 0.06%.
[0009] The brazing sheet configuration of the above identified
prior art documents are similar. Both are based on a core, an
intermediate braze metal which contains Mg and Bi, covered by a
thin covering layer. There is a potential risk with such a brazing
sheet structure. There might be a time lag between filler melting
and wetting. The influence of gravity on the melt can cause filler
flow under the surface oxide, resulting in inhomogeneous joint size
and large localised accumulations of molten filler.
[0010] The methods for fluxless brazing available in the prior art
have a constraint in that they require either an external covering
with higher melting temperature than the underlying braze, or is a
combination of two different braze alloy layers that are both
intended to melt during the brazing process. This does not allow
for simultaneous sophisticated corrosion potential gradient design,
high strength sheet design and joining without flux. There is also
a desire to improve the brazing process.
[0011] The demands from primarily the automotive industry are
increasing regarding the amount of residual flux that is allowed in
a heat exchanger system. It is difficult and costly to apply small
and repeatable flux amounts on localised areas on the internal
surfaces of a heat exchanger to repeatedly form high quality
internal joints and this invention provides a clear advantage in
that aspect of heat exchanger production.
[0012] Thus, there is still a need to provide a brazing sheet which
overcomes the above identified problems.
[0013] Other examples of previously known aluminium alloy brazing
sheets are known from U.S. Pat. No. 6,627,330 B1 and WO2010/052231,
which both disclose outermost layers with high or intentionally
added Mg content.
SUMMARY OF THE INVENTION
[0014] The objective of the present invention is to provide an
aluminium alloy brazing sheet that can be brazed in an inert or
reducing atmosphere, without the need to apply a flux, which
results in enhanced braze joints, and which allows sophisticated
corrosion potential design.
[0015] The object is achieved by the aluminium alloy brazing sheet
in accordance with independent claim 1. Embodiments are defined by
the dependent claims.
[0016] The aluminium alloy brazing sheet according to the present
invention is especially suitable for brazing to one or more
components other than the brazing sheet itself, in particular
brazing of fins or headers to the outer surface of a tube made from
the aluminium brazing sheet.
[0017] The aluminium alloy brazing sheet comprises an aluminium
alloy core material covered by an interlayer of an aluminium alloy,
which in turn is covered by an Al--Si braze alloy. The aluminium
alloy of the interlayer comprises .ltoreq.1.0% Si and 0.1-2.5% Mg,
preferably .gtoreq.0.2% Mg, more preferably .gtoreq.0.3% Mg, even
more preferably .gtoreq.0.5% Mg. The Al--Si braze alloy comprises
5-14% Si and 0.01-1.0% Bi, preferably 0.05-0.5% Bi, most preferably
0.07-0.2% Bi, .ltoreq.0.8% Fe, .ltoreq.6% Zn, .ltoreq.0.1% Sn,
.ltoreq.0.1% In, .ltoreq.0.3% Cu, .ltoreq.0.15% Mn, .ltoreq.0.05%
Sr, and unavoidable impurities each in amounts less than 0.05 wt-%
and a total impurity content of less than 0.2 wt-%, the balance
consisting of aluminium. The core material and the interlayer has a
higher melting temperature than the braze alloy.
[0018] The present invention is thus based on a completely
different brazing sheet configuration than described in for example
EP1306207B1 and WO2008/155067A1 to achieve good brazeability
without flux in controlled atmosphere and added corrosion
protection, and circumvents the possible limitations of the prior
art.
[0019] According to one embodiment, the aluminium alloy of the
interlayer comprises at least 0.9% Mg.
[0020] According to yet another embodiment, the aluminium alloy of
the interlayer comprises at most 2.2% Mg.
[0021] In accordance with one embodiment, the interlayer is
directly adjacent the core material, i.e. without any intermediate
layer between the interlayer and the core material. According to
another embodiment, the braze layer is directly adjacent the
interlayer, i.e. without any intermediate layer between the braze
layer and the interlayer. According to yet another embodiment, the
interlayer is sandwiched between the core layer and the braze alloy
without any additional layers between the core layer and the braze
alloy.
[0022] The aluminum alloy brazing sheet is used to produce brazed
products, such as heat exchangers.
[0023] Since no flux is present on the outside surfaces of the heat
exchanger produced from the brazing sheet according to the
invention any difficulties in detachment of flux residue that may
enter e.g. the passenger compartment of the vehicle are avoided.
This also improves the visual appearance of the heat exchanger.
Since no flux is present on the internal surfaces of the heat
exchanger any difficulties in clogging, erosion, and chemical
reactions between flux and cooling media and other perceived
drawbacks with flux residue is avoided.
[0024] There is also a clear cost advantage to be had in brazing
heat exchanger units without the use of flux as it eliminates not
only the cost of the flux itself but also shortens the lead time
through the brazing line, allows for lower labour costs, liberates
floor space in the factory, decreases demands on maintenance of
brazing hardware and decreases demands on housekeeping. Also,
important benefits are to be had in a better working environment
for people, less disposal of solid waste and waste water from the
fluxing system and smaller amounts of harmful gaseous effluents
from the brazing process.
DETAILED DESCRIPTION OF THE INVENTION
[0025] The aluminium alloy brazing sheet of the present invention
consists of an aluminium based core, covered on one or two sides by
a Mg-rich aluminium alloy as an interlayer which in turn is covered
by an Al--Si braze alloy, where said braze contains an addition of
Bi. The liquidus temperature of the Al--Si braze alloy is lower
than the solidus temperature of the core and the interlayer, which
has a higher liquidus temperature than the highest allowed brazing
temperature. The Mg from the interlayer should diffuse out to the
external surface of the braze during the heating up to brazing
temperature. If a correct amount of Mg arrives there and at the
correct time the oxide will be broken up to make it possible for
molten filler metal to wet any countersurface and form a joint,
while having an intact interlayer that assists in providing a
corrosion potential gradient through the thickness of the sheet
post brazing. In the present invention the Mg content of the filler
material, i.e. the braze material, is preferably <0.01%. The
present invention shows that optimum brazeability is achieved with
Mg in an interlayer between the core and the filler metal.
[0026] The invention is hereafter described as a three layered
aluminium alloy brazing sheet where brazing occurs on one side of
the sheet. However, the invention can be used to create braze
joints on both sides of the core, in which case the brazing sheet
will be built up by five layers. It can also be covered by a
sacrificial waterside on one side and be a four layered sheet or a
waterside with an interlayer between the core and the waterside
cladding that will provide a five layered sheet.
[0027] The present invention provides an aluminium alloy brazing
sheet product comprising: a core material covered by a Mg-rich
interlayer which in turn is covered by an Al--Si alloy which
contains Bi to enhance the brazing performance, where the said core
material and the interlayer has a higher melting temperature than
the brazing alloy and indeed higher melting temperatures than the
intended brazing temperature. The Mg from the interlayer diffuses
through the braze layer out to the external surface of the braze
during the heating up to brazing temperature. If a correct amount
of Mg arrives there and at the correct time the superficial oxide
will be broken up to make it possible for molten filler metal to
wet any countersurface and form a joint, while having an intact
interlayer that assists in providing a corrosion potential gradient
through the thickness of the sheet post brazing. To allow a good
joint to be formed in a heat exchanger the braze should melt at
around 577.degree. C. and the heating may reach temperatures in the
interval of 585-610.degree. C. Normally, one tends to aim in the
interval of 595-605.degree. C. This necessitates that the liquidus
of the interlayer and core layer be higher and they should both
have liquidus temperatures in excess of 615.degree. C.
The Braze Alloy
[0028] The Al--Si braze alloy preferably contains at most 0.02% Mg,
more preferably <0.01% Mg in order to obtain a good brazing. It
is important that the Mg content in the thin braze layer is kept
low in order to avoid excessive growth of oxides on the surface
during heating before brazing. The addition of Bi into the braze
layer according to the present invention enhances joint formation,
so that the joint is formed more rapidly and has a larger size. It
may also contain Zn, Sn and In that decrease the corrosion
potential of aluminium alloys or Cu and Mn that increase the
corrosion potential. Sr is a powerful modifier to achieve a small
Si particle size and can also be present in technologically
motivated amounts of up to 500 ppm.
[0029] The amount of Si in the Al--Si braze alloy can be chosen to
suit the special brazing process desired and is usually between 5
and 14% Si, but preferably 7 to 13% Si is used.
[0030] A preferred composition of the Al--Si braze alloy thus
contains [0031] Si 5 to 14%, preferably 7 to 13%, [0032]
Mg<0.02%, preferably <0.01%, [0033] Bi 0.01 to 1.0%,
preferably 0.05 to 0.5%, most preferably 0.07 to 0.2%, [0034]
Fe.ltoreq.0.8% [0035] Cu.ltoreq.0.3%, [0036] Mn.ltoreq.0.15%,
[0037] Zn.ltoreq.6%, [0038] Sn.ltoreq.0.1% [0039] In.ltoreq.0.1%
[0040] Sr.ltoreq.0.05%, and unavoidable impurities each in amounts
less than 0.05% and a total impurity content of less than 0.2%, the
balance consisting of aluminium.
The Core Material
[0041] The brazing sheet of the present invention can be used with
any aluminium brazing sheet core material. A suitable core material
can be any AA3xxx series alloy. It has been found within the
present invention that joint formation in brazing works well also
with Mg added to the core alloy, which means that the core can be
given a higher strength. The core should also contain Mn for
strength, brazability and corrosion performance and Cu to modify
the corrosion performance and for post-brazed strength. It can also
contain Si for strength and dispersoid formation purposes as well
as Ti for strength, corrosion and as grain refiner in casting. The
elements of Zr, Cr, V and Sc can be present for strength
modification and as dispersoid forming purposes.
[0042] Hence the core alloy preferably contains [0043] Mn<2.0%,
[0044] Cu.ltoreq.1.2%, [0045] Fe.ltoreq.1.0%, [0046]
Si.ltoreq.1.0%, [0047] Ti.ltoreq.0.2%, [0048] Mg.ltoreq.2.5%,
preferably 0.03-2.0% [0049] Zr, Cr, V and/or Sc.ltoreq.0.2% in
total, and unavoidable impurities each in amounts less than 0.05%
and a total impurity content of less than 0.2%, the balance
consisting of aluminium.
The Interlayer
[0050] The thin interlayer consists of an aluminium alloy, having a
melting point higher than the melting point of the covering Al--Si
braze metal, will need to contain a substantial amount of Mg to
allow diffusion through the superficial braze to break up oxide on
the superficial surface. The interlayer should therefore have a
Mg-content higher than 0.1%, and more preferably higher than 0.2%.
The most preferred case is that Mg is added to the alloy in amounts
of 0.3% or more, most preferably more than 0.5%. The joint
formation is feasible with 0.5% in the interlayer, as shown in the
examples. It is however significantly better with at least 0.9% Mg
in the interlayer. The rollability of the material may be difficult
when the Mg content of the interlayer exceeds 2.5%. Preferably, the
maximum content of Mg in the interlayer does not exceed 2.2%. Thus,
the Mg content of interlayer is 0.1-2.5%, preferably 0.2-2.5%, more
preferably 0.3-2.5%, even more preferably 0.5-2.5%, and most
preferably 0.9-2.2%. The interlayer may also contain Si, Mn, Fe,
Ti, Cu, Zn, Cr, Zr, V and Sc for the same reasons as the core
material. Zn, Sn and In may be included to decrease the corrosion
potential of the alloy and to help create a suitable post-brazed
corrosion potential gradient through the thickness of the
sheet.
[0051] The interlayer alloy thus preferably contains, [0052] Mg
0.1-2.5%, preferably .gtoreq.0.2%, more preferably .gtoreq.0.3%,
even more preferably .gtoreq.0.5%, most preferably 0.9-2.2% [0053]
Mn<2.0%, [0054] Cu.ltoreq.1.2%, [0055] Fe.ltoreq.1.0%, [0056]
Si.ltoreq.1.0%, [0057] Ti.ltoreq.0.2%, [0058] Zn.ltoreq.6%, [0059]
Sn.ltoreq.0.1%, [0060] In.ltoreq.0.1%, [0061] Zr, Cr, V and/or
Sc.ltoreq.0.2% in total, and unavoidable impurities each in amounts
less than 0.05%, and a total impurity content of less than 0.2%,
the balance consisting of aluminium.
The Composite Brazing Sheet
[0062] By the provision of an aluminium alloy brazing sheet product
comprising: a core material covered by an interlayer comprising Mg,
which in turn is covered by an Al--Si alloy which contains Bi to
enhance the brazing performance, where the said core material and
the interlayer has a higher melting temperature than the brazing
alloy and indeed higher melting temperatures than the intended
brazing temperature. The brazing sheet can be effectively brazed in
controlled atmosphere without the use of flux. The opposite side
can be unclad, arranged in a similar configuration, clad with a
sacrificial cladding, or an Al--Si braze cladding. However, the
brazing sheets that can be used within the present invention are
not limited to the above configurations.
[0063] The total thickness of the aluminium brazing sheet is in
between 0.1 and 4 mm, which is suitable in the manufacture of heat
exchangers. The thickness of the interlayer is preferably 5 to 200
.mu.m, so as to provide effective oxide disruption during brazing.
The thickness of the braze layer may be between 5 and 100 .mu.m.
The total clad layer thickness relative to the total thickness of
the multi layered brazing sheet is preferably of 3 to 30%. The
thickness of the braze is chosen so that sufficient filler is
available to provide adequate post-brazed joint size. Also, the
thickness should be chosen such that a suitable amount of Mg will
diffuse through the braze layer to the outer oxide during the braze
heating, thereby providing adequate oxide break-up and good
wetting. The thickness of the interlayer relative to the braze
alloy layer is between 25% and 250%, with most applications
requiring a thickness ratio expected in the interval of 50% to
150%. The suitable temperature interval at which the brazing is
being carried out is in the range of 580.degree. C. to 610.degree.
C., and preferably 590.degree. C. to 605.degree. C.
[0064] The chemistry of the interlayer and cores should be chosen
such that they after brazing provide a suitable corrosion potential
gradient. This means that the interlayer should be suitably
sacrificial to the core.
[0065] The sheet design is ideally such that a sufficient amount of
Mg should reach the oxide/metal interface to break up the oxide at
the right time during the braze heating cycle. If too much Mg
reaches the oxide/metal interface too early during the braze
heating cycle the excess Mg may assist in producing a too thick
oxide and prevent wetting and joint growth. If too little Mg
reaches the oxide/metal interface or if it arrives too late during
the braze heating cycle the wetting and joint growth will be
incomplete or absent. This is because the filler may flow
underneath the layer of unbroken oxide. Therefore, the braze
heating cycle is very important and should be considered together
with the sheet design, the thermomechanical production route,
furnace characteristics and the remaining heat exchanger assembly
design to provide a successful fluxfree brazing outcome.
[0066] The invention further provides a heat exchanger comprising
the aluminium alloy brazing sheet as described above.
Production of the Brazing Sheet
[0067] Each of the above described alloys may be cast using direct
chill (DC) casting or continuous twin roll casting or cast
continuously in a belt casting machine. The choice of casting
technique is decided by technical, economical and capacity
considerations. The core alloy is cast as a slab using a DC casting
route, whereas the intermediate layer and the outer thin layer is
cast using either DC casting or continuous casting techniques.
[0068] The predominant technique used today is DC casting and then
the slabs of the braze alloy ingot and the interlayer alloy ingot
are both scalped and then heated in a furnace to a temperature
between 350 and 550.degree. C. and the duration at the soaking
temperature varies from 0 to 20 hours. Subsequently both alloys are
hot rolled to the desired thickness and cut to suitable lengths.
The interlayer plate is then placed on the scalped surface of the
core ingot and the braze alloy plate is then placed on the surface
of the interlayer. The plates are held in place on the core slab by
means of seam welds along two opposite sides by means of MIG
welding, or by means of steel banding or by other suitable
techniques to make a manageable ingot package. The package is then
placed into a preheating furnace. The package is heated to a
temperature between 350.degree. C. and 550.degree. C. and the
duration at the soaking temperature is between 0 and 20 hours.
After that the clad package is hot rolled, cold rolled to final
dimension, stretched to improve flatness and slit to delivery
width. Intermediate and final heat treatments to achieve easier
production and the correct delivery temper is done as needed.
EXAMPLES
[0069] All alloys of the examples were cast using laboratory
casting equipment into so-called book moulds producing small slabs
with length 150 mm, width 90 mm and thickness 20 mm. The chemical
compositions of the alloys tested for brazeability can be seen in
table 1.
[0070] Each slab was scalped, heated from room temperature to
450.degree. C. during 8 hours, soaked at 450.degree. C. for 2 hours
and cooled in ambient air. Then the materials were rolled to a
suitable thickness and soft annealed between passes when necessary
to facilitate easy rolling. Then core-, intermediate braze
layer-and outer layer materials were combined to make three layer
clad packages where the layers were attached to each other by means
of cold rolling. The materials were cold rolled to of 0.25 mm
thickness, which provided a single side cladding with 10%
interlayer and 10% braze layer, with intermediate soft annealings
when necessary to provide easy rolling and given a final back
annealing to an H24 temper to provide large recrystallized grains
in the core during the subsequent brazing procedure. Instead of
temper annealing one may provide worked tempers, e.g. H12, H14 or
H112, to provide large recrystallized grains.
TABLE-US-00001 TABLE 1 Chemical compositions in weight-% of tested
alloys from melt analyses with OES. Al- loy Type Si Fe Cu Mn Mg Ti
Zr Bi A Core 0.14 0.50 0.12 1.09 <0.01 0.02 <0.01 <0.01 B
Core 0.07 0.22 0.81 1.70 <0.01 0.05 0.14 <0.01 C Core/ 0.75
0.22 0.29 0.60 0.31 0.15 <0.01 <0.01 interlayer D Core 0.68
0.25 0.30 0.03 0.42 0.14 <0.01 <0.01 E Core/ 0.05 0.20 0.28
1.30 0.22 0.02 <0.01 <0.01 interlayer F Core/ 0.50 0.22
<0.01 0.06 0.67 0.01 <0.01 <0.01 interlayer G Interlayer
0.05 0.17 <0.01 <0.01 0.51 <0.01 <0.01 <0.01 H
Interlayer 0.03 0.15 <0.01 <0.01 0.96 <0.01 <0.01
<0.01 I Interlayer 0.03 0.15 <0.01 <0.01 1.9 <0.01
<0.01 <0.01 J Interlayer 0.07 0.28 <0.01 0.80 1.1 <0.01
<0.01 <0.01 K Interlayer 0.09 0.33 <0.01 1.7 1.0 <0.01
<0.01 <0.01 L Interlayer 0.05 0.17 <0.01 <0.01 <0.01
<0.01 <0.01 <0.01 M Braze 10.0 0.23 <0.01 0.01 1.26
<0.01 <0.01 0.09 N Braze 10.2 0.17 <0.01 <0.01 0.11
<0.01 <0.01 0.12 O Braze 8.0 0.18 <0.01 <0.01 <0.01
<0.01 <0.01 0.11 P Braze 8.0 0.18 <0.01 <0.01 <0.01
<0.01 <0.01 <0.01 Q Braze 10.2 0.17 <0.01 <0.01
<0.01 <0.01 <0.01 0.12
[0071] The brazing was made in a laboratory glass furnace with
approximately 3 dm.sup.3 brazing chamber. The furnace was flushed
with nitrogen during the entire brazing cycle with a rate of 10
standard litres per minute. The brazing cycle was a linear heating
from room temperature to 600.degree. C. in 10 minutes, soaking for
3 minutes at 600.degree. C. followed by cooling in air to room
temperature. The sample set-up was a simple unclad bent angle on
coupon where the clad materials were used as coupon and an unclad
AA3003 with 0.5 mm gauge was used as the angle. All brazing was
made unfluxed. The samples were examined by visual examination of
the braze joints and a representative selection of some of the
results is given below.
TABLE-US-00002 TABLE 2 selected experimental results Inter- Comment
Core layer Braze Result Ex 1 Compara- B -- P No joining between
clad Standard tive coupon and unclad angle. CAB sheet Ex 2 Compara-
A -- M No joining between clad Standard tive coupon and unclad
angle. vacuum brazing sheet. Ex 3 Inventive B G O Joint formed
between clad coupon and unclad angle. Small. Ex 4 Inventive C H Q
Joint formed between clad coupon and unclad angle. Ex 5 Inventive D
I O Joint formed between clad coupon and unclad angle. Ex 6
Inventive E J Q Joint formed between clad coupon and unclad angle.
Ex 7 Inventive F K O Joint formed between clad coupon and unclad
angle. Ex 8 Compara- B G N No joining, too much Mg tive in braze Ex
9 Inventive B C O Joint formed between clad coupon and unclad
angle, very slightly sluggish. Ex 10 Inventive B E O Joining, but
reluctantly Ex 11 Inventive B F O Joint formed between clad coupon
and unclad angle. Ex 12 Compara- F K P No joining, no Bi in tive
braze Ex 13 Compara- B L O No joining, no Mg in tive interlayer
* * * * *